Intrusion alarm systems have been devised under a broad number of schemes ranging from a dog that barks to ultra sophisticated systems designed for the protection of highly valuable property and produced at commensurate cost. When developing any of the intrusion alarm systems, the design approach generally is premised upon a need to apprise one entity of the passage and, preferably, attempted passage of another entity across a selected portal or vulnerable boundary.
The effectiveness of alarm designs has, to the present, been predicated upon the degree of sophistication, redundancy and/or number of separate components for the system contemplated. As alarm system designs have evolved for broadened, higher volume markets, their sophistication has given way to the extent that the sensing techniques utilized tend toward either the primitive or specialized-monofunctional and the logic of alarm control is reduced to affording the operator only few alternatives, i.e., the devices are more readily compromised. For instance, intrusion alarm devices intended for the relatively higher volume, popularly priced market have been seen to utilize simple switches mounted on the inside of a door to detect a successful unauthorized entry. Such sensing does not enjoy the capability for detecting and alerting to an attempted entry. For such a function, sensing components must be capable of exhibiting a very high degree of sensitivity to minor impact or similarly generated phenomena. Where an alarm is sounded at a mere attempted entry, the occupant within the area of alert is afforded the most valuable of surveillance service -- the maximum available time interval to react to undertake protective measures.
To remain practical for higher volume markets, all such sensing devices should be easily calibrated to accommodate for an obviously broad range of sensing conditions. For instance, environmental "noise" conditions such as vibration and the like must be easily accounted for.
To simplify gaining access through a door protected by a simplified alarm, resort often is made to designs permitting an alarm delay following the triggering thereof. Thus the operator may enter an alarm supervised door and, within the delay interval, disarm the alarm by throwing an arm switch or the like. To be effective in this form, the delay period must be relatively short and the resetting technique should be relatively difficult to ascertain by anyone but the operator.
Coded entrance arrangements heretofore have been proposed wherein a switching code or key system is mounted at the outer side of a protected door and which, when properly actuated, remotely disarm an alarm system. Such systems, however, generally are too complex for manufacture and installation under high volume procedures suited to achieve popular price levels. For instance, the devices may be required to be mounted and wired within a wall. Alternately, complexities are encountered in protecting otherwise exposed wiring extending from one side of a door to another.
Another aspect to be considered in providing a practical alarm system suited for popular utilization resides in the degree of installation expertise required of the purchaser. A most advantageous system is one which requires no mounting or assembly expertise whotsoever; for instance, no wiring or sensor switch installation, and equally simple access accessory installation.